Because of their finite reserves, global petroleum resources are running out. With many developing countries currently industrializing, petroleum demand has sharply increased, causing an imbalance between market demand and supply and leading to an era of high oil prices. Furthermore, the reckless use of petroleum has brought about an explosive increase in greenhouse gases, provoking significant environmental problems such as global warming.
Extensive worldwide efforts have long been made to use biomass, which is regenerable and sustainable, as an alternative to petroleum resources. As a result, biofuels, such as bioethanol, biodiesel, etc. and bioplastic monomers, such as lactic acid, propanediol, etc., are successfully produced on an industrial scale and are used as substitutes for transportation fuels or petrochemical materials.
In recent years, intensive attention has been paid to 5-hydroxymethyl-2-furfural (HMF), a furan compound, as it has been discovered to be producible via conversion of biomass-derived carbohydrates.
Through oxidation, HMF can be converted into 2,5-furan dicarboxylic acid (FDCA), a known alternative to terephthalic acid (TPA). TPA is a monomer of poly(ethylene terephthalate) (PET). PET, which is used in a wide spectrum of fields including food and beverage containers, is synthesized through polycondensation between the monomers ethylene glycol (EG) and terephthalic acid (TPA). For the synthesis of biomass-based PET, its monomers EG and TPA should be derived from biomass. Currently, EG is industrially produced from bioethanol-based bioethylene. As for TPA, its synthesis based on biomass has not yet been achieved.
Recently, HMF has aroused keen interest for its use as a core intermediate for bioplastics and biofuels. Extensive studies have been directed toward the mass production of HMF, but none have yet succeeded in developing processes for the industrial mass production of HMF.
DMSO (dimethyl sulfoxide) is known as the most effective solvent for use in the conversion of fructose into HMF. HMF can be produced at excellent yield when fructose is heated for 1˜2 hrs at 80˜150° C. under an acidic condition in DMSO. However, the direct extraction of HMF from the DMSO solvent is difficult not only because DMSO is difficult to remove by distillation due to its high boiling point of 189° C., but also because DMSO is miscible with most solvents.
To avoid such problems, a strategy was suggested in which the conversion is conducted in a bicomponent system consisting of DMSO and a different solvent, with the real-time extraction of HMF from the solvent system (G. W. Huber, J. N. Chheda, C. J. Barrett, J. A. Dumesic, Science 2005, 308, 1446). However, only a limited amount of HMF can be extracted from the solvent system, and the solvent cannot be reused.
In place of DMSO, alternatives have been employed, such as DMF for its lower boiling point (G. A. Halliday, R. J. Young, V. V. Grushin, Org. Lett. 2003, 5, 2003) and ionic liquid for easy extraction of the product (H. B. Zhao, J. E. Holladay, H. Brown, Z. C. Zhang, Science, 2007, 316, 1597). However, DMF still has a high boiling point (153° C.) and ionic liquid is economically unfavorable for use in industrial mass production due to its high price.
Industrially, fructose is obtained from glucose through a catalytic process, and is marketed as a syrup containing about 20˜30 wt % of water. The direct use of a fructose in syrup form for HMF conversion is expected to reduce the cost of drying fructose into powder.